1. Field of the Invention
The present invention relates to an image processing function of an electronic endoscope apparatus. Particularly, the present invention relates to a sharpness adjustment function for adjusting the sharpness of an image.
2. Description of the Related Art
A sharpness enhancement method for enhancing the sharpness of an image by emphasizing or suppressing each frequency component included in an image signal by a degree which is different from each other for each frequency is well known (please refer to U.S. Pat. No. 5,739,922, for example).
An image (hereinafter, referred to as an endoscopic image) obtained by an electronic endoscope is an image of a body cavity. Therefore, the entire area of the image has a similar color. There is a possibility that all kinds of color existing in nature are included in a photograph of a person, landscape, or the like. However, only the color of the mucous membrane or a test agent may be included in the endoscopic image. Further, since no clear boundary is present in the body cavity, the endoscopic image does not include an object which may be classified as an edge. Further, when sharpness enhancement processing is performed on a photograph of a person or the like, the processing is performed to improve the image quality of the whole image of the photograph. However, when sharpness enhancement processing is performed on the endoscopic image, the processing is performed to emphasize information which is necessary for diagnosis in many cases.
The method disclosed in U.S. Pat. No. 5,739,922 may be applied to image processing of the electronic endoscope apparatus. However, since the image processing of the electronic endoscope apparatus is different from other image processing, as described above, more sophisticated sharpness adjustment method which is appropriate for image processing of the electronic endoscope apparatus is desired.